public class IsSameTree {
    class TreeNode {
        int val;
        TreeNode left;
        TreeNode right;
    }
    public boolean isSameTree(TreeNode p, TreeNode q) {
        if (p == null && q != null ||
                p != null && q == null)
            return false;
        if (p == null && q == null) return true;
        if (p.val != q.val) return false;
        return isSameTree(p.left, q.left) && isSameTree(p.right, q.right);
    }
}
